Protist ecology in Patagonian peatlands: pH, organic phosphorus, and sulfate as key drivers of testate amoeba diversity in undisturbed ecosystems

Peatlands in southern Chile, particularly in the remote Aysén region, are unique ecosystems that remain understudied despite their ecological significance as natural laboratories. These near-pristine environments serve as essential water reservoirs and harbor largely unexplored microbial diversity. Testate amoebae, a group of shelled protists, play key roles in nutrient cycling and are highly sensitive to environmental changes, making them valuable bioindicators. However, the ecological drivers shaping their diversity and community composition in Chilean peatlands remain poorly understood. This study investigated the spatial distribution and diversity of testate amoebae across five peatlands in the Aysén region (44°S and 49°S; Southern Patagonia, Chile). We recorded 73 morphospecies, including typical southern taxa such as Alocodera cockayni, Apodera vas, Argynnia gertrudeana, Certesella certesi, and C. martiali. Redundancy analysis revealed that organic phosphorus, pH, and sulfate are the most influential factors shaping testate amoeba communities. Beta diversity analysis indicated significant spatial turnover among sites, suggesting that local environmental gradients strongly influence species distribution. Interestingly, Sphagnum-dominated peatlands exhibited higher diversity compared to those with mixed vegetation (vascular plants and bryophytes). Our findings fill a critical gap in understanding microbial biodiversity in Chilean peatlands and highlight the importance of conserving these ecosystems as reservoirs of microbial diversity and natural archives of environmental change.